What This GameCube Keychain Mod Is and Why It Matters
This GameCube controller mod is a DIY controller project that converts a tiny plastic keychain into fully functional, plug-and-play miniature gaming hardware using an RP2040 microcontroller and custom 3D-printed internals. Maker Brux started with a Backpack Buddies GameCube controller keychain, a collectible that mimics the shape, feel, and movement of the original pad. Instead of keeping it as a fidget toy, he opened the shell and set out to turn it into a genuine input device the console would recognize. The challenge was the miniscule interior: there was barely enough room for switches, wiring, or a board. Solving that problem required surface-mount components, ultra-thin enameled wire, and careful trimming of the plastic shell. The result is a keychain that still looks like a novelty but behaves like a real controller you can slip into your pocket.
Hollowing the Shell and Designing Tiny 3D-Printed Mounts
The first technical hurdle was carving out usable space inside the keychain shell. Brux separated the two halves and discovered that the interior plastic left almost no room for standard components. Using a rotary tool and careful handwork, he chiseled away extra plastic to create a cleaner cavity without weakening the outer case. From there, he designed and 3D-printed custom mounting parts that aligned exactly with the original button positions. These mounts provide flat, repeatable surfaces for the surface-mount tactile switches that turn each plastic button press into an electrical input. Because there is no traditional PCB, the printed parts double as both mechanical supports and pseudo-boards. According to TechEBlog, these tiny printed components “barely held the switches in place,” which highlights how tight the tolerances are when building functional miniature gaming hardware inside an off-the-shelf keychain.
Wiring Buttons and Analog Stick to the RP2040 Microcontroller
With the mounts in place, Brux focused on translating physical movement into electrical signals using ultra-compact parts. Each button sits over a surface-mount tactile switch, soldered to ultra-thin enameled wire that routes back to a small RP2040 microcontroller board. The RP2040 acts as the brain for this GameCube controller mod, reading every button press as well as analog stick movement. For the stick, Brux added a set of tiny sensors capable of detecting motion in multiple directions, recreating the familiar analog feel within a keychain-sized housing. He also trimmed the internal posts on each button so they would fit over the new switches and still offer a clean click. The wiring is deliberately minimal and tightly routed so that when the two shell halves close, there are no bulges, gaps, or pinched conductors—a crucial detail for both durability and aesthetics.
Connecting to a Real GameCube with an Authentic Cable
To make the miniature controller behave like an original accessory, Brux needed a genuine cable and connector. He disassembled an official GameCube controller, stripping it down until only the wire and plug remained. That authentic connector is what lets the keychain plug directly into any GameCube port or compatible adapter without a separate interface. The RP2040 microcontroller sits between the internal inputs and this original cable, encoding signals in the format the console expects so the system thinks a full-size controller is attached. The wire exits the tiny shell cleanly, mirroring the look of the original hardware instead of a crude DIY breakout. In video demos, the controller successfully plays games such as Fortnite and Mario Kart, proving that a novelty keychain can become a practical gaming peripheral when paired with careful engineering and smart firmware.
From Prototype to Future Mini Controllers
Brux’s RP2040-powered mini pad is more than a one-off curiosity; it is a proof-of-concept for a whole family of tiny controllers. The same mix of 3D-printed internals, surface-mount switches, and slim wiring can be extended to other shells, as long as they have enough internal volume for an RP2040 microcontroller and basic inputs. In his video, Brux teases several follow-up builds, including miniature N64, SNES, and 3DS controllers created from similar keychain accessories. XDA notes that these projects highlight how capable RP2040-based boards can be in small-format devices when paired with creative mechanical design. For hobbyists, this DIY controller project shows that novelty items, fidget toys, and collectibles can often hide the foundations of working hardware. With careful planning, they can evolve into pocket-sized controllers that plug straight into classic consoles or modern adapters.
